An animal model of hemophagocytic lymphohistiocytosis (HLH): CD8+ T cells and interferon gamma are essential for the disorder

Human CD34+ Hematopoietic Stem Cell-Engrafted NSG Mice: Morphological and Immunophenotypic Features

Immunodeficient mice engrafted with human immune cells represent an innovative tool to improve translatability of animal models for the study of human diseases. Immunophenotyping in these mice focuses on engraftment rates and cellular differentiation in blood and secondary lymphoid organs, and is predominantly carried out by FACS (fluorescent activated cell sorting) analysis; information on the morphological aspects of engraftment and the prevalence of histologic lesions is limited. We histologically examined 3- to 6-month-old NSG mice, naïve or engrafted with CD34⁺ human hemopoietic stem cells (HSC), and employed a quantitative immunohistochemical approach to identify human and murine cell compartments, comparing the results with the FACS data. NSG mice mainly exhibited incidental findings in lungs, kidneys, testes, and adrenal glands. A 6-month-old NSG mouse had a mediastinal lymphoblastic lymphoma. The lymphoid organs of NSG mice lacked typical lymphoid tissue architecture but frequently exhibited small periarteriolar leukocyte clusters in the spleen. Mice engrafted with human HSC frequently showed nephropathy, ovarian atrophy, cataract, and abnormal retinal development, lesions considered secondary to irradiation. In addition, 20% exhibited multisystemic granulomatous inflammatory infiltrates, dominated by human macrophages and T cells, leading to the observed 7% mortality and morbidity. Immunophenotypic data revealed variable repopulation of lymphoid organs with hCD45⁺ human cells, which did not always parallel the engraftment levels measured via FACS. The study describes the most common pathological features in young NSG mice after human HSC engraftment. As some of these lesions contribute to morbidity, morphological assessment of the engraftment at tissue level might help improve immunophenotypic evaluations of this animal model.

Clinical analysis of macrophage activation syndrome in adult rheumatic disease: A multicenter retrospective study

AIM

To evaluate the clinical and laboratory characteristics, prognostic factors, and outcome of adult rheumatic disease-associated macrophage activation syndrome (MAS).

METHOD

A multicenter retrospective study was performed across 4 tertiary hospitals in China between January 1, 2017 to December 31, 2019.

RESULTS

There were 61 rheumatic disease patients with MAS enrolled into this retrospective clinical study. Fever and hyperferritinemia are the most frequent clinical feature and laboratory abnormality in MAS patients. Serum ferritin > 6000 ng/mL (odds ratio [OR] = 9.46, 95% CI = 2.53-47.13, P = .005) and hemophagocytosis in bone marrow smear (OR = 11.12, 95%, CI = 3.29-50.65, P = .001) were the 2 most prominent predictive factors indicating MAS occurrence. The 90-day all-cause mortality rate of all rheumatic disease patients with MAS was 22.9% (hazards ratio [HR] = 2.15, 95% CI = 0.81-6.78, P = .05). Platelets < 100 × 10⁹ /L (HR = 3.23, 95% CI = 2.51-4.81, P = .01) and ferritin > 6000ng/mL (HR = 6.12, 95% CI = 2.93-16.27, P = .005) were independent predictors of poor outcome in rheumatic disease-associated MAS.

CONCLUSION

Macrophage activation syndrome could be a fatal complication in rheumatic disease. Patients presenting with unexplained fever, serum ferritin > 6000 ng/mL, hepatosplenomegaly and cytopenia at baseline should raise the suspicion of MAS. The presence of serum ferritin > 6000 ng/mL, hepatosplenomegaly and low number of platelets was associated with poor outcome.

COVID-19: Transmission, prevention, and potential therapeutic opportunities

The novel coronavirus disease (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global challenge. Despite intense research efforts worldwide, an effective vaccine and viable treatment options have eluded investigators. Therefore, infection prevention, early viral detection and identification of successful treatment protocols provide the best approach in controlling disease spread. In this review, current therapeutic options, preventive methods and transmission routes of COVID-19 are discussed.

Human Autoinflammatory Diseases Mediated by NLRP3-, Pyrin-, NLRP1-, and NLRC4-Inflammasome Dysregulation Updates on Diagnosis, Treatment, and the Respective Roles of IL-1 and IL-18

Recent research has led to novel findings in inflammasome biology and genetics that altered the diagnosis and management of patients with autoinflammatory syndromes caused by NLRP3-, Pyrin-, NLRP1-, and NLRC4-inflammasomes and spurred the development of novel treatments. The use of next-generation sequencing in clinical practice allows for rapid diagnosis and the detection of somatic mutations that cause autoinflammatory diseases. Clinical differences in patients with NLRP3, pyrin, and NLRP1 inflammasomopathies, and the constitutive elevation of unbound free serum IL-18 that predisposes to the development of macrophage activation syndrome (MAS) in patients with gain-of function mutations in NLRC4 led to the screening and the characterization of novel diseases presenting with constitutively elevated serum IL-18 levels, and start to unravel the biology of "high IL-18 states" that translate into the use of biomarkers that improve diagnosis and monitoring of disease activity and investigations of treatments that target IL-18 and IFN-gamma which promise to improve the management and outcome of these conditions. Lastly, advances in structural modeling by cryo-electron microscopy (cryo-EM) of gasdermin, and of NLRP3- and NLRC4-inflammasome assembly, and the characterization of post-translational modifications (PTM) that regulate inflammasome activation, coupled with high-throughput screening (HTS) of libraries of inflammasome-inhibiting compounds, promise a new generation of treatments for patients with inflammasome-mediated diseases.

Common Sources of Inflammation and Their Impact on Hematopoietic Stem Cell Biology

Purpose of Review

Inflammatory signals have emerged as critical regulators of hematopoietic stem cell (HSC) function. Specifically, HSCs are highly responsive to acute changes in systemic inflammation and this influences not only their division rate but also their lineage fate. Identifying how inflammation regulates HSCs and shapes the blood system is crucial to understanding the mechanisms underpinning these processes, as well as potential links between them.

Recent Findings

A widening array of physiologic and pathologic processes involving heightened inflammation are now recognized to critically affect HSC biology and blood lineage production. Conditions documented to affect HSC function include not only acute and chronic infections but also autoinflammatory conditions, irradiation injury, and physiologic states such as aging and obesity.

Summary

Recognizing the contexts during which inflammation affects primitive hematopoiesis is essential to improving our understanding of HSC biology and informing new therapeutic interventions against maladaptive hematopoiesis that occurs during inflammatory diseases, infections, and cancer-related disorders.

JAK/STAT pathway inhibition sensitizes CD8 T cells to dexamethasone-induced apoptosis in hyperinflammation

Cytokine storm syndromes (CSS) are severe hyperinflammatory conditions characterized by excessive immune system activation leading to organ damage and death. Hemophagocytic lymphohistiocytosis (HLH), a disease often associated with inherited defects in cell-mediated cytotoxicity, serves as a prototypical CSS for which the 5-year survival is only 60%. Frontline therapy for HLH consists of the glucocorticoid dexamethasone (DEX) and the chemotherapeutic agent etoposide. Many patients, however, are refractory to this treatment or relapse after an initial response. Notably, many cytokines that are elevated in HLH activate the JAK/STAT pathway, and the JAK1/2 inhibitor ruxolitinib (RUX) has shown efficacy in murine HLH models and humans with refractory disease. We recently reported that cytokine-induced JAK/STAT signaling mediates DEX resistance in T cell acute lymphoblastic leukemia (T-ALL) cells, and that this could be effectively reversed by RUX. On the basis of these findings, we hypothesized that cytokine-mediated JAK/STAT signaling might similarly contribute to DEX resistance in HLH, and that RUX treatment would overcome this phenomenon. Using ex vivo assays, a murine model of HLH, and primary patient samples, we demonstrate that the hypercytokinemia of HLH reduces the apoptotic potential of CD8 T cells leading to relative DEX resistance. Upon exposure to RUX, this apoptotic potential is restored, thereby sensitizing CD8 T cells to DEX-induced apoptosis in vitro and significantly reducing tissue immunopathology and HLH disease manifestations in vivo. Our findings provide rationale for combining DEX and RUX to enhance the lymphotoxic effects of DEX and thus improve the outcomes for patients with HLH and related CSS.

Comparison of serum cytokine profiles in macrophage activation syndrome complicating different background rheumatic diseases in children

Objectives

To compare the cytokines involved in the development of macrophage activation syndrome (MAS) in different background rheumatic diseases and to identify serum biomarkers for MAS diagnosis.

Methods

Serum neopterin, IL-6, IL-18 and soluble TNF receptor (sTNFR) type I (sTNFR-I) and type II (sTNFR-II) levels were determined using ELISA in 12 patients with SLE, including five with MAS; 12 patients with JDM, including four with MAS; 75 patients with Kawasaki disease (KD), including six with MAS; and 179 patients with systemic JIA (s-JIA), including 43 with MAS. These results were compared with the clinical features of MAS.

Results

Serum neopterin, IL-18 and sTNFR-II levels were significantly higher during the MAS phase than during the active phase in patients with all diseases. Furthermore, serum sTNFR-I levels were significantly higher during the MAS phase than during the active phase in patients with SLE, KD and s-JIA. Receiver operating characteristic (ROC) curve analysis revealed that serum sTNFR-I levels for SLE, serum IL-18 levels for JDM, and serum sTNFR-II levels for KD and s-JIA had the highest areas under the ROC curve. Serum levels of these cytokines were significantly and positively correlated with serum ferritin levels.

Conclusions

Overproduction of IFN-γ, IL-18 and TNF-α might be closely related to the development of MAS. Serum levels of sTNFR-I for SLE, IL-18 for JDM, and sTNFR-II for KD and s-JIA might be useful diagnostic markers for the transition from active phase to MAS.

Hemophagocytic Lymphohistiocytosis: Lessons Learned from the Dark Side

Hemophagocytic lymphohistiocytosis (HLH) is a rare but severe form of immune dysregulation often presenting as unremitting fever, cytopenia, hepatosplenomegaly, coagulopathy, and elevation of typical HLH biomarkers. HLH is universally fatal, if left untreated. The HLH-2004 criteria are widely used to diagnose this condition, but there is growing concerns across different settings that its application may result in undertreatment of certain patients. There is an expanding spectrum of genetic conditions that can be complicated by HLH. This review summarizes the current concepts in HLH, the lessons learned from the past, and provide an overview of the latest diagnostic and treatment modalities.

Changes in Cytokine Profile during Initial Treatment of Pediatric Hemophagocytic Lymphohistiocytosis Associated with Epstein-Barr Virus

Hemophagocytic lymphohistiocytosis (HLH) associated with Epstein-Barr virus (EBV) infection can be self-limiting, severe/aggressive, or fatal. We report a case of EBV-HLH with persistent fever, severe pancytopenia, hypertriglyceridemia, and hypofibrinogenemia in a 4-year-old boy. Levels of plasma cytokines and chemokines were measured with a Bio-Plex system at 1, 2, 3, 4, 5, and 8 days after hospital admission. Administration of steroid and high-dose intravenous immunoglobulin (1 g/kg) did not alleviate fever or reduce cytokine production; however, after administration of etoposide (an antineoplastic agent), fever decreased immediately, the patient's general condition improved, and levels of IL-6, IL-10, IL-8, MCP-1, IFN-γ, and TNF-α declined after etoposide administration. In particular, IFN-γ production sharply declined, from 1,104.1 pg/mL to 101.5 pg/mL, and IL-6 level decreased from 229.8 pg/mL to 11.0 pg/mL, on the day after initial etoposide administration. There was no later recurrence of symptoms during treatment with dexamethasone, etoposide, and cyclosporine A. This case suggests that early etoposide administration is critical for treatment success and indicates that etoposide promptly inhibits cytokine production.

Successful treatment of secondary macrophage activation syndrome with emapalumab in a patient with newly diagnosed adult-onset Still's disease: case report and review of the literature

Here, we present a 22-year-old female patient with adult-onset Still's disease (AOSD) who was newly diagnosed in the setting of secondary macrophage activation syndrome (MAS), a rare, life-threatening inflammatory disease with 50% mortality due to multi-organ failure. She met the diagnostic criteria of AOSD and MAS, while genetic testing excluded primary causes of MAS. She had high fevers, anemia, thrombocytopenia, splenomegaly, hematophagocytosis, and elevated serum ferritin (37,950 ng/mL) and CD25 levels (11,870 pg/mL), which remained unresponsive to corticosteroids and anakinra. Her serum interferon gamma (IFN-γ) levels were elevated (7 pg/mL). She was markedly responsive to IFN-γ blockade with emapalumab that eliminated her fevers and all MAS-associated laboratory abnormalities. This report provides initial evidence for therapeutic efficacy for IFN-γ blockade in AOSD and secondary MAS.

Trigger-dependent differences determine therapeutic outcome in murine primary hemophagocytic lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (FHL) is a hyperinflammatory syndrome affecting patients with genetic cytotoxicity defects. Perforin-deficient (PKO) mice recapitulate the full clinical picture of FHL after infection with lymphocytic choriomeningitis virus (LCMV). Hyperactivated CD8⁺ T cells and IFN-γ have been identified as the key drivers of FHL and represent targets for therapeutic interventions. However, the response of patients is variable. This could be due to trigger-dependent differences in pathogenesis, which is difficult to address in FHL patients, since the trigger frequently escapes detection. We established an alternative FHL model using intravenous infection of PKO mice with murine CMV (MCMV)_Smith . PKO mice developed acute FHL after both infections and fulfilled HLH diagnostic criteria accompanied by excessive IFN-γ production by disease-inducing T cells, that enrich in the BM. However, direct comparison of the two infection models disclosed trigger-dependence of FHL progression and revealed a higher contribution of CD4 T cells and NK cells to IFN-γ production after MCMV infection. Importantly, therapeutic intervention by IFN-γ neutralization or CD8⁺ T-cell depletion had less benefit in MCMV-triggered FHL compared to LCMV-triggered FHL, likely due to MCMV-induced cytopathology. Thus, the context of the specific triggering viral infection can impact the success of targeted immunotherapeutic HLH control.

Cell Versus Cytokine - Directed Therapies for Hemophagocytic Lymphohistiocytosis (HLH) in Inborn Errors of Immunity

Hemophagocytic lymphohistiocytosis (HLH) is a heterogeneous hyperinflammatory syndrome with different pathways of pathogenesis resulting in similar clinical presentations. It is best defined and understood if presenting in the context of genetic immunodeficiencies associated with defects of lymphocyte cytotoxicity. In these "primary" forms of HLH, cellular and soluble immune effectors are relatively well characterized. While etoposide-based broad cell-directed therapies remain standard of care, more specific therapies targeting these effectors individually are increasingly available. Anti-CD52 as a cell-directed therapy and anti-IFN-gamma, IL-18BP, and JAK-inhibition as cytokine-directed therapies are expected to broaden the therapeutic options, but the precise role of these drugs in first-line and rescue treatment indications remains to be defined. A number of additional inborn errors of immunity are associated with episodes of immune activation fulfilling the clinical criteria of HLH. Impaired pathogen control is a key driver of hyperinflammation in some conditions, while others are characterized by a strong autoinflammatory component. This heterogeneity of disease-driving factors and the variable severity in disease progression in these conditions do not allow a simple adaptation of protocols established for "primary" HLH to HLH in the context of other inborn errors of immunity. Cytokine-directed therapies hold significant promise in these increasingly recognized disorders.

Emapalumab in Children with Primary Hemophagocytic Lymphohistiocytosis

BACKGROUND

Primary hemophagocytic lymphohistiocytosis is a rare syndrome characterized by immune dysregulation and hyperinflammation. It typically manifests in infancy and is associated with high mortality.

METHODS

We investigated the efficacy and safety of emapalumab (a human anti-interferon-γ antibody), administered with dexamethasone, in an open-label, single-group, phase 2-3 study involving patients who had received conventional therapy before enrollment (previously treated patients) and previously untreated patients who were 18 years of age or younger and had primary hemophagocytic lymphohistiocytosis. The patients could enter a long-term follow-up study until 1 year after allogeneic hematopoietic stem-cell transplantation or until 1 year after the last dose of emapalumab, if transplantation was not performed. The planned 8-week treatment period could be shortened or extended if needed according to the timing of transplantation. The primary efficacy end point was the overall response, which was assessed in the previously treated patients according to objective clinical and laboratory criteria.

RESULTS

At the cutoff date of July 20, 2017, a total of 34 patients (27 previously treated patients and 7 previously untreated patients) had received emapalumab; 26 patients completed the study. A total of 63% of the previously treated patients and 65% of the patients who received an emapalumab infusion had a response; these percentages were significantly higher than the prespecified null hypothesis of 40% (P = 0.02 and P = 0.005, respectively). In the previously treated group, 70% of the patients were able to proceed to transplantation, as were 65% of the patients who received emapalumab. At the last observation, 74% of the previously treated patients and 71% of the patients who received emapalumab were alive. Emapalumab was not associated with any organ toxicity. Severe infections developed in 10 patients during emapalumab treatment. Emapalumab was discontinued in 1 patient because of disseminated histoplasmosis.

CONCLUSIONS

Emapalumab was an efficacious targeted therapy for patients with primary hemophagocytic lymphohistiocytosis. (Funded by NovImmune and the European Commission; NI-0501-04 and NI-0501-05 ClinicalTrials.gov numbers, NCT01818492 and NCT02069899.).

Hemophagocytic lymphohistiocytosis: An update on pathogenesis, diagnosis, and therapy

Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening state of immune hyperactivation that arises in the setting of genetic mutations and infectious, inflammatory, or neoplastic triggers. Sustained, aberrant activation of cytotoxic CD8⁺ T cells and resultant inflammatory cytokine release are core pathogenic mechanisms. Key clinical features include high persistent fever, hepatosplenomegaly, blood cytopenia, elevated aminotransferase and ferritin levels, and coagulopathy. HLH is likely under-recognized, and mortality remains high, especially in adults; thus, prompt diagnosis and treatment are essential. Familial forms of HLH are currently treated with chemotherapy as a bridge to hematopoietic stem cell transplantation. HLH occurring in rheumatic disease (macrophage activation syndrome) is treated with glucocorticoids, IL-1 blockade, or cyclosporine A. In other forms of HLH, addressing the underlying trigger is essential. There remains a pressing need for more sensitive, context-specific diagnostic tools. Safer, more effective therapies will arise with improved understanding of the cellular and molecular mechanisms of HLH.

Emapalumab for the treatment of relapsed/refractory hemophagocytic lymphohistiocytosis

Emapalumab is a fully human immunoglobulin G1 monoclonal antibody directed against interferon-γ (IFN-γ), which in November 2018 received the first global approval for the treatment of pediatric and adult patients with primary hemophagocytic lymphohistiocytosis (HLH) with refractory, recurrent, or progressive disease or intolerance to HLH therapy. This review will highlight the pathophysiology of primary HLH, the therapeutic rationale for use of IFN-γ-targeting therapy, and potential limitations to its broader use in the treatment of HLH.

A research-driven approach to the identification of novel natural killer cell deficiencies affecting cytotoxic function

Natural killer cell deficiencies (NKDs) are an emerging phenotypic subtype of primary immune deficiency. NK cells provide a defense against virally infected cells using a variety of cytotoxic mechanisms, and patients who have defective NK cell development or function can present with atypical, recurrent, or severe herpesviral infections. The current pipeline for investigating NKDs involves the acquisition and clinical assessment of patients with a suspected NKD followed by subsequent in silico, in vitro, and in vivo laboratory research. Evaluation involves initially quantifying NK cells and measuring NK cell cytotoxicity and expression of certain NK cell receptors involved in NK cell development and function. Subsequent studies using genomic methods to identify the potential causative variant are conducted along with variant impact testing to make genotype-phenotype connections. Identification of novel genes contributing to the NKD phenotype can also be facilitated by applying the expanding knowledge of NK cell biology. In this review, we discuss how NKDs that affect NK cell cytotoxicity can be approached in the clinic and laboratory for the discovery of novel gene variants.

Signaling pathways involved in the T-cell-mediated immunity against Epstein-Barr virus: Lessons from genetic diseases

Primary immunodeficiencies (PIDs) provide researchers with unique models to understand in vivo immune responses in general and immunity to infections in particular. In humans, impaired immune control of Epstein-Barr virus (EBV) infection is associated with the occurrence of several different immunopathologic conditions; these include non-malignant and malignant B-cell lymphoproliferative disorders, hemophagocytic lymphohistiocytosis (HLH), a severe inflammatory condition, and a chronic acute EBV infection of T cells. Studies of PIDs associated with a predisposition to develop severe, chronic EBV infections have led to the identification of key components of immunity to EBV - notably the central role of T-cell expansion and its regulation in the pathophysiology of EBV-associated diseases. On one hand, the defective expansion of EBV-specific CD8 T cells results from mutations in genes involved in T-cell activation (such as RASGRP1, MAGT1, and ITK), DNA metabolism (CTPS1) or co-stimulatory pathways (CD70, CD27, and TNFSFR9 (also known as CD137/4-1BB)) leads to impaired elimination of proliferating EBV-infected B cells and the occurrence of lymphoma. On the other hand, protracted T-cell expansion and activation after the defective killing of EBV-infected B cells is caused by genetic defects in the components of the lytic granule exocytosis pathway or in the small adapter protein SH2D1A (also known as SAP), a key activator of T- and NK cell-cytotoxicity. In this setting, the persistence of EBV-infected cells results in HLH, a condition characterized by unleashed T-cell and macrophage activation. Moreover, genetic defects causing selective vulnerability to EBV infection have highlighted the role of co-receptor molecules (CD27, CD137, and SLAM-R) selectively involved in immune responses against infected B cells via specific T-B cell interactions.

Priorities for Improving Outcomes for Nonmalignant Blood Diseases: A Report from the Blood and Marrow Transplant Clinical Trials Network

Nonmalignant blood diseases such as bone marrow failure disorders, immune dysregulation disorders, and hemoglobinopathies often lead to shortened life spans and poor quality of life. Many of these diseases can be cured with allogeneic hematopoietic cell transplantation, but patients are often not offered the procedure because of perceived insufficient efficacy and/or excess toxicity. In 2018, the Blood and Marrow Transplant Clinical Trials Network convened a task force to identify the most urgently needed yet feasible clinical trials with potential to improve the outcomes for patients with nonmalignant diseases. This report summarizes the task force discussions and specifies the network plans for clinical trial development for nonmalignant blood diseases.

Macrophage Activation Syndrome and Secondary Hemophagocytic Lymphohistiocytosis in Childhood Inflammatory Disorders: Diagnosis and Management

Macrophage activation syndrome (MAS), a form of secondary hemophagocytic lymphohistiocytosis, is a frequently fatal complication of a variety of pediatric inflammatory disorders. MAS has been most commonly associated with systemic juvenile idiopathic arthritis (sJIA), as approximately 10% of children with sJIA develop fulminant MAS, with another 30-40% exhibiting a more subclinical form of the disease. Children with other rheumatologic conditions such as systemic lupus erythematosus and Kawasaki disease are also at risk for MAS. Moreover, MAS also complicates various genetic autoinflammatory disorders such as gain of function mutations in the cytosolic inflammasome NLRC4, pediatric hematologic malignancies (e.g., T-cell lymphoma), and primary immunodeficiencies characterized by immune dysregulation. Disease-specific and broadly inclusive diagnostic criteria have been developed to facilitate the diagnosis of MAS. Recently, simple screening tools such as the serum ferritin to erythrocyte sedimentation rate ratio have been proposed. Early diagnosis and rapid initiation of immunosuppression are essential for the effective management of MAS. With a better understanding of the pathophysiology of MAS and the advent of novel therapeutics, a broad immunosuppressive approach to treatment is giving way to targeted anti-cytokine therapies. These treatments include agents that block interleukin-1 (IL-1), IL-6, IL-18, interferon-γ, as well as inhibitors of downstream targets of cytokine signaling (e.g., Janus kinases). Increased early recognition of MAS among pediatric inflammatory disorders combined with the use of effective and less toxic cytokine-targeted therapies should lower the mortality of this frequently fatal disorder.

Treatment of refractory hemophagocytic lymphohistiocytosis with emapalumab despite severe concurrent infections

Neutralization of IFN-γ with emapalumab can reverse severe, refractory hemophagocytic lymphohistiocytosis. Neutralizing IFN-γ did not impair control of multiple viral and other infections in a severely ill patient.

Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis in a small child: A case report

INTRODUCTION

Hemophagocytic lymphohistiocytosis (HLH) is a rare, potentially lethal disorder, characterized by a dysregulation of the immune response, leading to a severe inflammatory syndrome. Epstein-Barr virus (EBV)-associated HLH is a form of secondary HLH, a fulminant presentation of an otherwise benign viral infection.

PATIENT CONCERNS

We report the case of a 3-year-old girl who presented with fever, signs of accute upper respiratory tract infection and spontaneous, disseminated ecchymoses. Initial laboratory tests revealed pancytopenia. A bone marrow aspirate was performed, which revealed megaloblasts and numerous macrophages, with abundant foamy cytoplasm. Megaloblastic anemia was excluded, as the levels of vitamin B12 and folic acid were both within normal ranges.

DIAGNOSIS

Hyperferritinemia, hypertriglyceridemia, hypofibrinogenemia, and splenomegaly were relevant criteria for the diagnosis of HLH, in accordance with the bone marrow specimen. Positive immunoglobulin M antibodies for EBV were supportive of an acute EBV infection, which was the most probable trigger of HLH. The patient's evolution was complicated by a massive epistaxis, in the context of thrombocytopenia which required plasma, thrombocyte, and erythrocyte substitutes.

INTERVENTION

The patient was started on a treatment regimen of 8 weeks with etoposide and dexamethasone.

OUTCOME

Her evolution was favorable, the treatment being successful in remission induction.

CONCLUSION

Our case emphasizes the diagnostic challenges of HLH, in a patient with EBV infection whose evolution was hindered by a severe epistaxis, with potentially fatal outcome.

Diacylglycerol Kinase ζ Regulates Macrophage Responses in Juvenile Arthritis and Cytokine Storm Syndrome Mouse Models

Dysregulation of monocyte and macrophage responses are often observed in children with systemic juvenile idiopathic arthritis (sJIA) and cytokine storm syndrome (CSS), a potentially fatal complication of chronic rheumatic diseases. Both conditions are associated with activation of TLR signaling in monocyte and macrophage lineage cells, leading to overwhelming inflammatory responses. Despite the importance of TLR engagement in activating proinflammatory macrophages, relatively little is known about activation of intrinsic negative regulatory pathways to attenuate excessive inflammatory responses. In this study, we demonstrate that loss of diacylglycerol (DAG) kinase (Dgk) ζ, an enzyme which converts DAG into phosphatidic acid, limits inflammatory cytokine production in an arthritic mouse model dependent on TLR2 signaling and in a CSS mouse model dependent on TLR9 signaling. In vitro, Dgkζ deficiency results in reduced production of TNF-α, IL-6, and IL-1β and in limited M1 macrophage polarization. Mechanistically, Dgkζ deficiency decreases STAT1 and STAT3 phosphorylation. Moreover, Dgkζ levels are increased in macrophages derived from mice with CSS or exposed to plasma from sJIA patients with active disease. Our data suggest that Dgkζ induction in arthritic conditions perpetuates systemic inflammatory responses mediated by macrophages and highlight a potential role of Dgkζ-DAG/phosphatidic acid axis as a modulator of inflammatory cytokine production in sJIA and CSS.

The interferon-gamma pathway is selectively up-regulated in the liver of patients with secondary hemophagocytic lymphohistiocytosis

Aim of this study was to investigate the activation of the IFNγ pathway in the affected liver and in the blood of patients with secondary hemophagocytic lymphohistiocytosis (sHLH). To this purpose, the mRNA expression levels of IFNG and IFNγ-inducible genes as well as Tyrosine (701)-phosphorylated signal transducer and activator of transcription 1 (STAT1) protein levels were evaluated in the liver and in peripheral blood mononuclear cells (PBMCs) of three patients with sHLH with predominant liver involvement. The mRNA expression levels of IFNG and IFNγ-inducible genes were markedly higher in patient livers compared to control livers and to one disease control liver. Conversely, slight differences in the expression levels of Type I IFN-inducible genes and other classical inflammatory cytokine genes were found. Further supporting the activation of the IFNγ pathway, higher protein levels of phosphorylated and total STAT1 were detected in patient livers compared to control livers. When the expression of the same genes analysed in liver tissues was evaluated in PBMCs collected from 2 out of 3 patients before the liver biopsy, we found that mRNA levels of IFNγ-inducible genes were markedly increased. Accordingly, high circulating levels of IFNγ-inducible CXCL9 were observed in patients. Altogether, these data demonstrate the selective and marked up-regulation of the IFNγ pathway in the liver tissue and blood of patients with active sHLH. Finally, we show that measurement of circulating CXCL9 levels and evaluation of IFNγ-inducible gene expression levels in PBMCs may represent a new valid tool to better identify patients with suspected HLH with predominant liver involvement.

Genetic Deficiency of Interferon-γ Reveals Interferon-γ-Independent Manifestations of Murine Hemophagocytic Lymphohistiocytosis

OBJECTIVE

Familial hemophagocytic lymphohistiocytosis (FHLH) is a complex cytokine storm syndrome caused by genetic abnormalities rendering CD8+ T cells and natural killer cells incapable of cytolytic killing. In murine models of FHLH, interferon-γ (IFNγ) produced by CD8+ T cells has been identified as a critical mediator of disease, and an IFNγ-blocking antibody (emapalumab) has recently been approved by the Food and Drug Administration. However, development of hemophagocytic lymphohistiocytosis (HLH)/macrophage activation syndrome (MAS) in patients who are genetically unresponsive to IFNγ questions the absolute necessity of IFNγ in driving disease. This study was undertaken to determine the necessity of IFNγ in driving HLH.

METHODS

IFNγ^-/- Prf1^-/- mice were infected with lymphocytic choriomeningitis virus (LCMV), and HLH immunopathologic features, including survival, weight loss, cytopenias, cytokine profiles, and immune cell phenotypes, were assessed. Mixed bone marrow chimeras were created to determine the immune cell-intrinsic role of IFNγ receptor signaling. CD8+ T cell depletion and interleukin-33 (IL-33)/ST2 blockade were performed using monoclonal antibodies.

RESULTS

LCMV infection of IFNγ^-/- Prf1^-/- mice resulted in severe HLH-like disease. CD8+ T cells and the IL-33/ST2 axis remained essential mediators of disease; however, IFNγ-independent HLH immunopathology correlated with a 10-15-fold increase in neutrophilia (P < 0.001) and an altered cytokine milieu dominated by IL-6, IL-1β, and granulocyte-macrophage colony-stimulating factor (GM-CSF) (P < 0.05). Furthermore, IFNγ regulated CD8+ T cell expression of GM-CSF and neutrophil survival.

CONCLUSION

IFNγ is not necessary for the development of fulminant HLH, requiring physicians to consider case-by-case treatment strategies. Use of therapies that target upstream activators of CD8+ T cells, such as IL-33/ST2 signaling, may be more universally applicable treatment options that ameliorate both IFNγ-dependent and -independent manifestations of HLH/MAS.

Interferon target-gene expression and epigenomic signatures in health and disease

Multiple type I interferons and interferon-γ (IFN-γ) are expressed under physiological conditions and are increased by stress and infections, and in autoinflammatory and autoimmune diseases. Interferons activate the Jak-STAT signaling pathway and induce overlapping patterns of expression, called 'interferon signatures', of canonical interferon-stimulated genes (ISGs) encoding molecules important for antiviral responses, antigen presentation, autoimmunity and inflammation. It has now become clear that interferons also induce an 'interferon epigenomic signature' by activating latent enhancers and 'bookmarking' chromatin, thus reprogramming cell responses to environmental cues. The interferon epigenomic signature affects ISGs and other gene sets, including canonical targets of the transcription factor NF-κB that encode inflammatory molecules, and is involved in the priming of immune cells, tolerance and the training of innate immune memory. Here we review the mechanisms through which interferon signatures and interferon epigenomic signatures are generated, as well as the expression and functional consequences of these signatures in homeostasis and autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis and systemic sclerosis.

Hemophagocytosis induced by Leishmania donovani infection is beneficial to parasite survival within macrophages

Visceral leishmaniasis (VL) is caused by parasitic protozoa of the genus Leishmania and is characterized by clinical manifestations such as fever, hepatosplenomegaly and anemia. Hemophagocytosis, the phenomenon of phagocytosis of blood cells by macrophages, is found in VL patients. In a previous study we established an experimental model of VL, reproducing anemia in mice for the first time, and identified hemophagocytosis by heavily infected macrophages in the spleen as a possible cause of anemia. However, the mechanism for parasite-induced hemophagocytosis or its role in parasite survival remained unclear. Here, we established an in vitro model of Leishmania-induced hemophagocytosis to explore the molecules involved in this process. In contrast to naïve RAW264.7 cells (mouse macrophage cell line) which did not uptake freshly isolated erythrocytes, RAW264.7 cells infected with L. donovani showed enhanced phagocytosis of erythrocytes. Additionally, for hemophagocytes found both in vitro and in vivo, the expression of signal regulatory protein α (SIRPα), one of the receptors responsible for the ‘don’t-eat-me’ signal was suppressed by post-transcriptional control. Furthermore, the overlapped phagocytosis of erythrocytes and Leishmania parasites within a given macrophage appeared to be beneficial to the parasites; the in vitro experiments showed a higher number of parasites within macrophages that had been induced to engulf erythrocytes. Together, these results suggest that Leishmania parasites may actively induce hemophagocytosis by manipulating the expression of SIRPα in macrophages/hemophagocytes, in order to secure their parasitism.

Parasites can manipulate host immune responses to build favorable environment to them. Because this parasite-driven immune modulation is often linked to symptoms in infected individuals, not only parasiticidal compounds but also immunological interventions limiting such the parasites’ abilities will serve as treatment options. In this study, we studied the mechanism and its role of hemophagocytosis (the phenomenon whereby macrophages engulf erythrocytes) caused by Leishmania donovani, a causative agent of VL. In vitro experiments revealed parasites have ability to directly disrupt macrophage’s recognition of self-cells, and that the induced engulfment of erythrocytes by L. donovani infection is beneficial to the parasites for their intracellular survival. These results suggest that Leishmania parasites actively induce hemophagocytosis by manipulating the ‘don’t-eat-me’ signal in macrophages for their survival. Although it is still to be determined how Leishmania parasites change the ‘don’t-eat-me’ signal in macrophages, our study may facilitate development of an immunotherapy which limits the change and lead to improvement of anemia due to hemophagocytosis as well as control of parasite survival.

Haemophagocytic lymphohisticytosis-an underrecognized hyperinflammatory syndrome

Haemophagocytic lymphohisticytosis (HLH) is a syndrome of uncontrolled, severe systemic inflammation (hyperinflammation) arising either from a genetic immune system defect [primary (pHLH)] or triggered as a complication of malignancy, infection, or rheumatologic disease [secondary (sHLH)]. Patients with HLH often have non-specific symptoms and become progressively and critically unwell, with fever, cytopenia and multi-organ failure. Untreated, HLH is almost universally fatal, but even when treated, mortality is high, particularly when HLH complicates malignancy. HLH is managed with immunosuppression, and this can seem difficult to justify in such unwell patients. This review aims to examine the diagnostic and treatment challenges posed by sHLH and to improve recognition among rheumatologists who, being expert in the management of multisystem diseases and in the use of immunosuppression, are ideally placed to deliver care and build an evidence base for better disease characterization and treatment.

Role of interferon-γ in immune-mediated graft failure after allogeneic hematopoietic stem cell transplantation

Pathophysiology of graft failure (GF) occurring after allogeneic hematopoietic stem cell transplantation (HSCT) still remains elusive. We measured serum levels of several different cytokines/chemokines in 15 children experiencing GF, comparing their values with those of 15 controls who had sustained donor cell engraftment. Already at day +3 after transplantation, patients developing GF had serum levels of interferon (IFN)-γ and CXCL9 (a chemokine specifically induced by IFNγ) significantly higher than those of controls (8859±7502 vs. 0 pg/mL, P=0.03, and 1514.0±773 vs. 233.6±50.1 pg/mlL, P=0.0006, respectively). The role played by IFNγ in HSCT-related GF was further supported by the observation that a rat anti-mouse IFNγ-neutralizing monoclonal antibody promotes donor cell engraftment in Ifngr1-/-mice receiving an allograft. In comparison to controls, analysis of bone marrow-infiltrating T lymphocytes in patients experiencing GF documented a predominance of effector memory CD8+ cells, which showed markers of activation (overexpression of CD95 and downregulation of CD127) and exhaustion (CD57, CD279, CD223 and CD366). Finally, we obtained successful donor engraftment in 2 out of 3 children with primary hemophagocytic lymphohistiocytosis who, after experiencing GF, were re-transplanted from the same HLA-haploidentical donor under the compassionate use coverage of emapalumab, an anti-IFNγ monoclonal antibody recently approved by the US Food and Drug Administration for treatment of patients with primary hemophagocytic lymphohistiocytosis. Altogether, these results suggest that the IFNγ pathway plays a major role in GF occurring after HSCT. Increased serum levels of IFNγ and CXCL9 represent potential biomarkers useful for early diagnosis of GF and provide the rationale for exploring the therapeutic/preventive role of targeted neutralization of IFNγ.

Challenges in the diagnosis of hemophagocytic lymphohistiocytosis: Recommendations from the North American Consortium for Histiocytosis (NACHO)

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of pathologic immune activation, often associated with genetic defects of lymphocyte cytotoxicity. Though a distinctive constellation of features has been described for HLH, diagnosis remains challenging as patients have diverse presentations associated with a variety of triggers. We propose two concepts to clarify how HLH is diagnosed and treated: within the broader syndrome of HLH, "HLH disease" should be distinguished from "HLH disease mimics" and HLH subtypes should be categorized by specific etiologic associations, not the ambiguous dichotomy of "primary" and "secondary." We provide expert-based advice regarding the diagnosis and initiation of treatment for patients with HLH, rooted in improved understanding of its pathophysiology.

Emapalumab: First Global Approval

Emapalumab-Izsg (hereafter referred to as emapalumab) [Gamifant^®] is a monoclonal antibody directed against interferon gamma that is available as an intravenous infusion. Emapalumab is being developed by Novimmune and Swedish Orphan Biovitrum for the treatment of haemophagocytic lymphohistiocytosis (HLH). In November 2018, emapalumab received its first global approval in the USA, for the treatment of paediatric (newborn and older) and adult patients with primary HLH, who have refractory, recurrent or progressive disease or intolerance to conventional HLH therapy. Emapalumab is under regulatory review in the EU for the treatment of primary HLH. This article summarizes the milestones in the development of emapalumab leading to this first global approval for HLH in the USA.

Ruxolitinib in adult patients with secondary haemophagocytic lymphohistiocytosis: an open-label, single-centre, pilot trial

BACKGROUND

Hemophagocytic lymphohistiocytosis is a cytokine-driven inflammatory syndrome that is associated with substantial morbidity and mortality. Overall survival in adult patients with secondary haemophagocytic lymphohistiocytosis remains suboptimal, and novel therapeutic strategies are needed. The phosphorylation-dependent activation of the Janus family kinases JAK1 and JAK2 are hallmarks of the final common pathway in this disease. We therefore aimed to determine the activity and safety of ruxolitinib, a JAK inhibitor, in adults with secondary haemophagocytic lymphohistiocytosis.

METHODS

We performed an open-label, single-centre, pilot study of ruxolitinib in adults with secondary haemophagocytic lymphohistiocytosis at the University of Michigan Rogel Cancer Center (Ann Arbor, MI, USA). We included patients aged 18 years or more who fulfilled at least five of the eight HLH-2004 criteria for hemophagocytic lymphohistiocytosis. Discontinuation of corticosteroids was not required for enrolment in this study. Patients received oral ruxolitinib (15 mg twice a day) on a continuous 28-day cycle, or until disease progression or unacceptable toxicity. The primary endpoint was overall survival at 2 months from the first dose of ruxolitinib. Secondary endpoints included the assessment of adverse events, response (defined as the assessment of all quantifiable signs and laboratory abnormalities included in the diagnostic criteria for haemophagocytic lymphohistiocytosis), and pharmacodynamic biomarkers. Analyses were done in all treated patients with available data. This study is registered with ClinicalTrials.gov, number NCT02400463, and is still recruiting.

FINDINGS

As of Feb 7, 2019, five patients had been enrolled. The first patient was enrolled in February, 2016. No deaths were recorded, with a median follow-up of 490 days (IQR 190-1075). 2-month overall survival was 100% (95% CI 57-100). Regarding response, resolution of symptoms (either partial or complete) and disease-associated laboratory abnormalities was observed in all five patients. Cytopenias improved in all patients within the first week of treatment, leading to relatively rapid transfusion independence, discontinuation of corticosteroids, and hospital discharge. A single serious adverse event (ie, grade 4 febrile neutropenia) was reported. One patient discontinued treatment because of grade 2 extremity pain and no treatment-related deaths were observed. Improvements in inflammatory markers (eg, ferritin, soluble IL-2 receptor) and T cells and monocytes activation (ie, decreased STAT1 phosphorylation) were observed following treatment.

INTERPRETATION

These preliminary data suggest that ruxolitinib is active, well tolerated, and manageable in the outpatient setting in patients with secondary haemophagocytic lymphohistiocytosis. Given the paucity of effective, non-myelosuppressive therapies, these preliminary findings have important therapeutic implications for patients with haemophagocytic lymphohistiocytosis and other cytokine-release syndromes and warrant further investigation.

FUNDING

National Cancer Institute, the University of Michigan Rogel Cancer Center, and Incyte Corporation.

Inborn Errors of Immunity With Immune Dysregulation: From Bench to Bedside

Inborn errors of immunity are genetic disorders with broad clinical manifestations, ranging from increased susceptibility to infections to significant immune dysregulation, often leading to multiple autoimmune phenomena, lymphoproliferation, and malignancy. The treatment is challenging as it requires careful balancing of immunosuppression in subjects at increased risk of infections. Recently, the improved ability to define inborn errors of immunity pathophysiology at the molecular level has set the basis for the development of targeted therapeutic interventions. Such a "precision medicine" approach is mainly bases on the use of available small molecules and biologics to target a specific cell function. In this article, we summarize the clinical and laboratory features of various recently described inborn errors of immunity associated with immune dysregulation and hyperinflammation in which mechanism-based therapeutic approaches have been implemented.

Comparison of serum biomarkers for the diagnosis of macrophage activation syndrome complicating systemic juvenile idiopathic arthritis

Our study aimed to compare the accuracy of serum biomarkers for the diagnosis of macrophage activation syndrome (MAS) complicating systemic juvenile idiopathic arthritis (s-JIA). Serum cytokine levels (neopterin, IL-18, and CXCL9 and soluble tumor necrosis factor receptor type I (sTNFR-I) and II) were determined by enzyme-linked immunosorbent assay in 78 patients with s-JIA, including 21 with MAS. Receiver operating characteristic curve analysis revealed area under the curve values and cut off values of neopterin, IL-18, CXCL9, sTNFR-II/I ratio and ferritin were 0.9465/19.5 nmol/l, 0.8895/69250 ng/ml, 0.9333/3130 pg/ml, 0.9395/3.796 and 0.8671/2560 ng/ml, respectively. Serum neopterin levels were significantly elevated in patients with MAS and those were correlated positively with disease activity. In conclusion, serum neopterin levels may be used as a promising indicator of disease activity in s-JIA and MAS and for evaluating it. It may also be a useful marker to diagnose the transition to MAS from active-phase s-JIA.

Chemokine Expression in Murine RPE/Choroid in Response to Systemic Viral Infection and Elevated Levels of Circulating Interferon-γ

Purpose

To examine how circulating immune mediators in vivo may affect gene and protein expression at the RPE/choroid interface.

Methods

Young mice were systemically infected with lymphocytic choriomeningitis virus (LCMV) or continuously infused with IFN-γ. RPE/choroid was isolated and analyzed with whole-transcriptome gene expression microarrays. Selected gene expression findings were validated at the protein level.

Results

Both the systemic immune activation from virus infection and the sterile systemically increased level of IFN-γ resulted in increased expression of chemokine ligands, chemokine receptors, and early complement components in isolates of RPE/choroid. These findings were largely absent from LCMV-infected mice deficient in either the interferon α/β receptor or IFN-γ.

Conclusions

Together, these findings demonstrate that acute systemic immune activation results in a local response at the RPE/choroid interface that may include chemokine-dependent recruitment of inflammatory cells and engagement of the complement system. This may represent a link between the systemic low-grade inflammation and the retinal pathology observed in several multifactorial entities such as aging, AMD, and diabetes.

Convergent pathways of the hyperferritinemic syndromes

Hyperferritinemia and pronounced hemophagocytosis help distinguish a subset of patients with a particularly inflammatory and deadly systemic inflammatory response syndrome. Two clinically similar disorders typify these hyperferritinemic syndromes: hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS). HLH is canonically associated with a complete disturbance of perforin/granzyme-mediated cytotoxicity, whereas MAS occurs in the context of the related rheumatic diseases systemic juvenile idiopathic arthritis and adult-onset Still's disease, with associated IL-1 family cytokine activation. In practice, however, there are accumulating lines of evidence for innate immune dysregulation in HLH as well as partial impairments of cytotoxicity in MAS, and these mechanisms likely represent only a fraction of the host and environmental factors driving hyperferritinemic inflammation. Herein, we present new findings that highlight the pathogenic differences between HLH and MAS, two conditions that present with life-threatening hyperinflammation, hyperferritinemia and hemophagocytosis.

Critically Severe Case of Neonatal Herpes with High Viral Load and Hemophagocytic Syndrome

Neonatal disseminated herpes simplex virus (HSV) infection is a severe disease with high mortality and morbidity; yet, the pathophysiology remains unclear. Here, we report a male infant with disseminated HSV type 1 (HSV-1) infection, complicated by hemophagocytic lymphohistiocytosis (HLH) and multiple organ failure. The infant, born at 39 weeks of gestation by normal delivery, developed fever (38.5˚C) with the high serum C-reactive protein levels on the 1st day of life, and exhibited tachypnea on the 3rd day. On the 5th day of life, the patient received mechanical ventilation and was transferred to our neonatal ICU. Real-time PCR for HSV-1 DNA revealed an extremely high serum concentration (1.0 × 10⁹ copies/µL), and he was diagnosed with HSV-1 infection. Acyclovir (ACV) and corticosteroid pulse therapies with methylprednisolone were started. Continuous hemodiafiltration (CHDF) using cytokine-absorbing hemofilters was also initiated because of renal failure. These therapies, however, failed to control the disease, and the patient died on the 41st day of life. The dose of ACV on CHDF might not be adequate, although we could not measure the serum ACV concentrations. After the patient's death, we measured his serum cytokine concentrations taken four times during the clinical course. Serum concentrations of interleukin (IL)-6, IL-10, IL-1β, and interferon (IFN)-γ were elevated at the time of admission and were remarkably decreased by 10 days after treatment. In particular, the concentrations of IL-1β and IFN-γ were lower than the measurable ranges. It is therefore important to measure serum cytokine concentrations in real time to prevent excessive immune suppression.

IFN-γ and CD25 drive distinct pathologic features during hemophagocytic lymphohistiocytosis

BACKGROUND

Inflammatory activation of CD8+ T cells can, when left unchecked, drive severe immunopathology. Hyperstimulation of CD8+ T cells through a broad set of triggering signals can precipitate hemophagocytic lymphohistiocytosis (HLH), a life-threatening systemic inflammatory disorder.

OBJECTIVE

The mechanism linking CD8+ T-cell hyperactivation to pathology is controversial, with excessive production of IFN-γ and, more recently, excessive consumption of IL-2, which are proposed as competing hypotheses. We formally tested the proximal mechanistic events of each pathway in a mouse model of HLH.

METHODS

In addition to reporting a complete autosomal recessive IFN-γ receptor 1-deficient patient with multiple aspects of HLH pathology, we used the mouse model of perforin (Prf1)KO mice infected with lymphocytic choriomeningitis virus to genetically eliminate either IFN-γ production or CD25 expression and assess the immunologic, hematologic, and physiologic disease measurement.

RESULTS

We found a striking dichotomy between the mechanistic basis of the hematologic and inflammatory components of CD8+ T cell-mediated pathology. The hematologic features of HLH were completely dependent on IFN-γ production, with complete correction after loss of IFN-γ production without any role for CD8+ T cell-mediated IL-2 consumption. By contrast, the mechanistic contribution of the immunologic features was reversed, with no role for IFN-γ production but substantial correction after reduction of IL-2 consumption by hyperactivated CD8+ T cells. These results were complemented by the characterization of an IFN-γ receptor 1-deficient patients with HLH-like disease, in whom multiple aspects of HLH pathology were observed in the absence of IFN-γ signaling.

CONCLUSION

These results synthesize the competing mechanistic models of HLH pathology into a dichotomous pathogenesis driven through discrete pathways. A holistic model provides a new paradigm for understanding HLH and, more broadly, the consequences of CD8+ T-cell hyperactivation, thereby paving the way for clinical intervention based on the features of HLH in individual patients.

Mechanisms of action of ruxolitinib in murine models of hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is an often-fatal disorder characterized by the overactivation of T cells and macrophages that excessively produce proinflammatory cytokines, including interferon-γ (IFN-γ). Previously, we reported that the JAK inhibitor ruxolitinib dampens T-cell activation and lessens inflammation in a model of HLH in which perforin-deficient (Prf1 ^-/-) mice are infected with lymphocytic choriomeningitis virus (LCMV). Ruxolitinib inhibits signaling downstream of IFN-γ, as well as several other JAK-dependent cytokines. As a consequence, it remained unclear whether ruxolitinib was exerting its beneficial effects in HLH by inhibiting IFN-γ signaling or by targeting signaling initiated by other proinflammatory cytokines. To address this question, we compared the effects of ruxolitinib with those obtained using an IFN-γ-neutralizing antibody (αIFN-γ) in 2 murine HLH models. In both models, ruxolitinib and αIFN-γ reduced inflammation-associated anemia, indicating that ruxolitinib operates in an IFN-γ-dependent manner to reverse this HLH manifestation. In contrast, the number and activation status of T cells and neutrophils, as well as their infiltration into tissues, were significantly reduced following treatment with ruxolitinib, but they remained unchanged or were increased following treatment with αIFN-γ. Notably, despite discontinuation of ruxolitinib, LCMV-infected Prf1 ^-/- mice exhibited enhanced survival compared with mice in which αIFN-γ was discontinued. This protective effect could be mimicked by transient treatment with αIFN-γ and a neutrophil-depleting antibody. Thus, ruxolitinib operates through IFN-γ-dependent and -independent mechanisms to dampen HLH by targeting the deleterious effects of T cells and neutrophils, with the latter representing an unappreciated and understudied cell type that contributes to HLH pathogenesis.

The inhibitory receptors on NK cells and CTLs are upregulated in adult and adolescent patients with secondary hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) includes primary HLH (pHLH) and secondary HLH (sHLH). Mutations that cause abnormal functions in natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) are frequently identified in pHLH. However, why NK cells and CTLs exhibit abnormal functions in sHLH remains unclear. Here, we demonstrated that NK cells in sHLH exhibited a high expression of inhibitory receptor NKG2A and a low expression of activating receptor NKG2D. Besides, the expression of HLA-E on lymphocyte, the adaptor of NKG2A on NK cells, was elevated in sHLH. Moreover, CTLs in sHLH patients expressed a higher level of functional exhaustion markers PD-1, TIM-3 and LAG-3 as well as a lower secretion of IFN-γ and CD107a upon stimulation. In addition, the expression of MHC-I on lymphocytes was decreased. Taken together, our study indicates a potentially pathological mechanism of sHLH and may open up new avenues for the development of immunotherapies against sHLH.

Plcγ2/Tmem178 dependent pathway in myeloid cells modulates the pathogenesis of cytokine storm syndrome

Cytokine storm syndrome (CSS) is a life-threatening condition characterized by excessive activation of T cells and uncontrolled inflammation, mostly described in patients with familial hemophagocytic lymphohistiocytosis and certain systemic auto-inflammatory diseases, such as systemic juvenile idiopathic arthritis (sJIA). Defects in T cell cytotoxicity as a mechanism for uncontrolled inflammation following viral infections fail to represent the whole spectrum of CSS. Evidence implicates dysregulated innate immune responses, especially activation of monocytes and macrophages, in patients with CSS. However, the direct contribution of monocytes/macrophages to CSS development and the signaling pathways involved in their activation have not been formally investigated. We find that depletion of monocytes/macrophages during early stages of CSS development, by clodronate-liposomes or neutralizing anti-CSF1 antibody, reduces mortality and inflammatory cytokine levels in two CSS mouse models, one dependent on T cells and the second induced by repeated TLR9 stimulation. We further demonstrate that activation of Plcγ2 in myeloid cells controls CSS development by driving macrophage pro-inflammatory responses. Intriguingly, the Plcγ2 downstream effector Tmem178, a negative modulator of calcium levels, acts in a negative feedback loop to restrain inflammatory cytokine production. Genetic deletion of Tmem178 leads to pro-inflammatory macrophage polarization in vitro and more severe CSS in vivo. Importantly, Tmem178 levels are reduced in macrophages from mice with CSS and after exposure to plasma from sJIA patients with active disease. Our data identify a novel Plcγ2/Tmem178 axis as a modulator of inflammatory cytokine production by monocytes/macrophages. We also find that loss of Tmem178 accentuates the pro-inflammatory responses in CSS.

Senescence-accelerated mice (SAMP1/TA-1) treated repeatedly with lipopolysaccharide develop a condition that resembles hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis is a life-threatening systemic hyperinflammatory disorder with primary and secondary forms. Primary hemophagocytic lymphohistiocytosis is associated with inherited defects in various genes that affect the immunological cytolytic pathway. Secondary hemophagocytic lymphohistiocytosis is not inherited, but complicates various medical conditions including infections, autoinflammatory/autoimmune diseases, and malignancies. When senescence-accelerated mice (SAMP1/TA-1) with latent deterioration of immunological function and senescence-resistant control mice (SAMR1) were treated repeatedly with lipopolysaccharide, SAMP1/TA-1 mice displayed the clinicopathological features of hemophagocytic lymphohistiocytosis such as hepatosplenomegaly, pancytopenia, hypofibrinogenemia, hyperferritinemia, and hemophagocytosis. SAMR1 mice showed no features of hemophagocytic lymphohistiocytosis. Lipopolysaccharide induced upregulation of proinflammatory cytokines such as interleukin-1β, interleukin-6, tumor necrosis factor-α, and interferon-γ, and interferon-γ-inducible chemokines such as c-x-c motif chemokine ligands 9 and 10 in the liver and spleen in both SAMP1/TA-1 and SAMR1 mice. However, upregulation of proinflammatory cytokines and interferon-γ-inducible chemokines in the liver persisted for longer in SAMP1/TA-1 mice than in SAMR1 mice. In addition, the magnitude of upregulation of interferon-γ in the liver and spleen after lipopolysaccharide treatment was greater in SAMP1/TA-1 mice than in SAMR1 mice. Furthermore, lipopolysaccharide treatment led to a prolonged increase in the proportion of peritoneal M1 macrophages and simultaneously to a decrease in the proportion of M2 macrophages in SAMP1/TA-1 mice compared with SAMR1 mice. Lipopolysaccharide appeared to induce a hyperinflammatory reaction and prolonged inflammation in SAMP1/TA-1 mice, resulting in features of secondary hemophagocytic lymphohistiocytosis. Thus, SAMP1/TA-1 mice represent a useful mouse model to investigate the pathogenesis of bacterial infection-associated secondary hemophagocytic lymphohistiocytosis.

Calm in the midst of cytokine storm: a collaborative approach to the diagnosis and treatment of hemophagocytic lymphohistiocytosis and macrophage activation syndrome

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) were historically thought to be distinct entities, often managed in isolation. In fact, these conditions are closely related. A collaborative approach, which incorporates expertise from subspecialties that previously treated HLH/MAS independently, is needed. We leveraged quality improvement (QI) techniques in the form of an Evidence-Based Guideline (EBG) to build consensus across disciplines on the diagnosis and treatment of HLH/MAS.

METHODS

A multidisciplinary work group was convened that met monthly to develop the HLH/MAS EBG. Literature review and expert opinion were used to develop a management strategy for HLH/MAS. The EBG was implemented, and quality metrics were selected to monitor outcomes.

RESULTS

An HLH/MAS clinical team was formed with representatives from subspecialties involved in the care of patients with HLH/MAS. Broad entry criteria for the HLH/MAS EBG were established and included fever and ferritin ≥500 ng/mL. The rheumatology team was identified as the "gate-keeper," charged with overseeing the diagnostic evaluation recommended in the EBG. First-line medications were recommended based on the acuity of illness and risk of concurrent infection. Quality metrics to be tracked prospectively based on time to initiation of treatment and clinical response were selected.

CONCLUSION

HLH/MAS are increasingly considered to be a spectrum of related conditions, and joint management across subspecialties could improve patient outcomes. Our experience in creating a multidisciplinary approach to HLH/MAS management can serve as a model for care at other institutions.

The Immunology of Macrophage Activation Syndrome

Synonymous with secondary hemophagocytic lymphohistiocytosis, macrophage activation syndrome (MAS) is a term used by rheumatologists to describe a potentially life-threatening complication of systemic inflammatory disorders, most commonly systemic juvenile idiopathic arthritis (sJIA) and systemic lupus erythematosus (SLE). Clinical and laboratory features of MAS include sustained fever, hyperferritinemia, pancytopenia, fibrinolytic coagulopathy, and liver dysfunction. Soluble interleukin-2 receptor alpha chain (sCD25) and sCD163 may be elevated, and histopathology often reveals characteristic increased hemophagocytic activity in the bone marrow (and other tissues), with positive CD163 (histiocyte) staining. A common hypothesis as to the pathophysiology of many cases of MAS proposes a defect in lymphocyte cytolytic activity. Specific heterozygous gene mutations in familial HLH-associated cytolytic pathway genes (e.g., PRF1, UNC13D) have been linked to a substantial subset of MAS patients. In addition, the pro-inflammatory cytokine environment, particularly IL-6, has been shown to decrease NK cell cytolytic function. The inability of NK cells and cytolytic CD8 T cells to lyse infected and otherwise activated antigen presenting cells results in prolonged cell-to-cell (innate and adaptive immune cells) interactions and amplification of a pro-inflammatory cytokine cascade. The cytokine storm results in activation of macrophages, causing hemophagocytosis, as well as contributing to multi-organ dysfunction. In addition to macrophages, dendritic cells likely play a critical role in antigen presentation to cytolytic lymphocytes, as well as contributing to cytokine expression. Several cytokines, including tumor necrosis factor, interferon-gamma, and numerous interleukins (i.e., IL-1, IL-6, IL-18, IL-33), have been implicated in the cytokine cascade. In addition to broadly immunosuppressive therapies, novel cytokine targeted treatments are being explored to dampen the overly active immune response that is responsible for much of the pathology seen in MAS.

Macrophage Activation-Like Syndrome: A Distinct Entity Leading to Early Death in Sepsis

Hemophagocytic lymphohistocytosis (HLH) is characterized by fulminant cytokine storm leading to multiple organ dysfunction and high mortality. HLH is classified into familial (fHLH) and into secondary (sHLH). fHLH is rare and it is due to mutations of genes encoding for perforin or excretory granules of natural killer (NK) cells of CD8-lymphocytes. sHLH is also known as macrophage activation syndrome (MAS). Macrophage activation syndrome (MAS) in adults is poorly studied. Main features are fever, hepatosplenomegaly, hepatobiliary dysfunction (HBD), coagulopathy, cytopenia of two to three cell lineages, increased triglycerides and hemophagocytosis in the bone marrow. sHLH/MAS complicates hematologic malignancies, autoimmune disorders and infections mainly of viral origin. Pathogenesis is poorly understood and it is associated with increased activation of macrophages and NK cells. An autocrine loop of interleukin (IL)-1β over-secretion leads to cytokine storm of IL-6, IL-18, ferritin, and interferon-gamma; soluble CD163 is highly increased from macrophages. The true incidence of sHLH/MAS among patients with sepsis has only been studied in the cohort of the Hellenic Sepsis Study Group. Patients meeting the Sepsis-3 criteria and who had positive HSscore or co-presence of HBD and disseminated intravascular coagulation (DIC) were classified as patients with macrophage activation-like syndrome (MALS). The frequency of MALS ranged between 3 and 4% and it was an independent entity associated with early mortality after 10 days. Ferritin was proposed as a diagnostic and surrogate biomarker. Concentrations >4,420 ng/ml were associated with diagnosis of MALS with 97.1% specificity and 98% negative predictive value. Increased ferritin was also associated with increased IL-6, IL-18, IFNγ, and sCD163 and by decreased IL-10/TNFα ratio. A drop of ferritin by 15% the first 48 h was a surrogate finding of favorable outcome. There are 10 on-going trials in adults with sHLH; two for the development of biomarkers and eight for management. Only one of them is focusing in sepsis. The acronym of the trial is PROVIDE (ClinicalTrials.gov NCT03332225) and it is a double-blind randomized clinical trial aiming to deliver to patients with septic shock treatment targeting their precise immune state. Patients diagnosed with MALS are receiving randomized treatment with placebo or the IL-1β blocker anakinra.